A Manhattan bond trader is fighting to keep alive a 3-year-old battle against his former lawyers and accountants, alleging they “conspired” to keep him away from a $15 million payday.

Drew Doscher — formerly of Seaport Global — was ousted from his job in 2013 after he discovered — and objected to — “multiple illegal trading schemes” at the investment bank, he claims in court papers.

Seaport maintained “a secret backbook,” which it used to operate its own hedge fund to “illegally ‘front-run’ ” clients’ trades, Doscher claims in the filing — elaborating for the first time on why he was allegedly tossed from the firm.

“After being asked by clients to buy or sell certain securities, the firm would execute its own trades in those securities to profit from the client’s impending trades,” Doscher said in an affidavit filed with court papers on Wednesday that seek to counter a move by his former lawyers and accountants to have his suit thrown out of court.

In his previous filing, Doscher was more obscure about the alleged improper activities at Seaport that led to his objections — and ultimate dismissal.

For example, in an earlier court filing Doscher claimed he “believed [his colleagues] violated the applicable Finra Front Running Policy at the time.”

Doscher commenced Finra arbitration against his former firm in 2014 to get his full partnership payout. Instead of getting $15 million plus interest, the distressed debt expert was only awarded $2.3 million, he claimed.

After his effort to obtain the larger payout failed, Doscher sued his legal eagles and CPAs — alleging the team of Sobel & Co. accountants and the lawyers at McMillan, Constabile, Maker & Perone improperly withheld 5,000 pages of evidence that would have proved his case for the larger payout.

The two firms withheld the documents on the instruction of Seaport, Doscher claims in his latest court filing, made Wednesday in Manhattan state court.